1. Field of the Invention
This invention relates to an agricultural tractor for carrying out a rotary cultivating operation and a plowing operation.
2. Description of the Related Art
An agricultural tractor includes a front wheel change speed device switchable between a standard state for driving dirigible front wheels at substantially the same speed as rear wheels, and an accelerating state for driving the front wheels at a higher speed than the rear wheels. A proposal has been made to provide the tractor with a front wheel speed control device for automatically switching the front wheel change speed device from the standard state to the accelerating state upon detection of the front wheels being steered in excess of a predetermined reference angle. Such a construction has been put to practical use as effective for enabling the tractor to make small turns near ridges without roughening the field.
In connection with this front wheel speed control, a technique has been developed for inhibiting the front wheel change speed device from switching to the accelerating state when the tractor runs faster than a predetermined reference speed. This prevents a small turn being made when the tractor is traveling at high speed.
Conditions for the above automatic front wheel speed control and inhibition of front wheel acceleration are determined based on a cultivating operation, which is a main operation, carried out with a rotary cultivator. These control and inhibition are canceled when carrying out an operation other than the rotary cultivating operation, such as a plowing operation.